New York City’s Mayor Bloomberg will have the satisfaction of his ban on large sugary drinks going into effect next Tuesday, and for some businesses it’ll be pretty easy: Don’t serve big sodas. There’s a potential headache coming on for baristas and coffee shop workers however, and it’s all because of a complicated tangle of milk, calories and sugar ratios included in the new rules. Better start taking notes.

For anyone ordering a coffee who wants to add their own sugar in at the condiment stand, that’ll be just fine, easy-peasy lemon squeezy. But many people order pre-sweetened drinks or want baristas to add sugar or flavored syrups when they order, a common practice at Dunkin’ Donuts and McDonald’s, notes the New York Times in its report on the new rules.

At Starbucks, some large drinks will escape the rules and can be more than 16 ounces as long as baristas add no more than three to five packets of sugar, depending on the size of the drink.

But those rules go straight out the window for anyone ordering a drink that contains more than 50% milk like a latte. Milk is viewed as healthy, so Bloomberg is down with that.

“This will have no impact on a large cup of joe, unless more than four packets of sugar are added,” said Samantha Levine, a city spokeswoman. “Real sweet tooths who want even more sugar can pour in as much as they like themselves.”

Instead of trying to find a way through the maze of rules on how much sugar a barista can add, McDonald’s and Dunkin’ Donuts say they’ll stop doing so altogether, and leave the sweet stuff up to customers.

“Our focus is on customer service and making sure that our crew know exactly what to do to comply with the ban,” said Cheryll Forsatz, a McDonald’s spokeswoman.

Meanwhile, Dunkin’ Donuts has tried to allay confusion by handing out fliers at cash registers titled “New N.Y.C. Regulations — What They Mean for You,” with explanations on what will happen, if anything, to customers’ drinks.

Smaller independent cafes won’t be able to sell large drinks with flavored sugary syrups included if they’re over the size limit, which means either serving the syrup on the side or just taking the drinks off the menu entirely.